Combined cycle power plants have demonstrated high thermal efficiency, reliability, and cost-effective power generation. A combined cycle power plant may include a combustion turbine, a steam generator, and a steam turbine. The steam turbine of a combined cycle power plant is powered by the steam generated by the hot exhaust of the combustion turbine in the steam generator.
This design results in different response times of the combustion and steam turbines. Whereas an increase in fuel supply to the combustion turbine may result in a nearly instantaneous corresponding power increase in the combustion turbine, the corresponding response of the steam turbine is delayed until the fuel is burned, and the steam is produced. Consequently, a combined cycle power plant may experience overall delays due to the delay of the bottoming cycle (steam turbine). In some situations, an increase in the frequency of a combined cycle power plant needs to satisfy primary frequency response requirements. To comply with the primary frequency response requirements, the combined cycle power plant operators may discount the steam turbine contribution altogether during frequency transitions. This approach may result in inefficient fuel consumption and stress on the overall combined cycle power plant operations.